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1,630,613 y 1927' w. G. GRAVES PROCESS OF DRYING AND CALCINING LITHOPHONE Filed Jan. 23, 1926 HYfer ,2? J9 14 PM,

r M 4 J 0 5 134/ ll 9 v 7 1 -7 I J? a 13 1 WM4 W atto'muga Patented Wlay 31, 1927.

UNITED STATES PATENT OFFICE.

WALTER GRAVES, OF CLEVELAND, OHIO, ASSIGNOR TO THE GRASSELLI CHEMICAL COMPANY, OF CLEVELAND, OHIO, A CORPORATION OF OHIO.

PROCESS OF DRYING AND CALCINING LITHOPONE.

Application filed January 23, 1926. Serial No. 83,304.

The invention relates to the drying or heating or the drying and heating of materials, and particularly to the continuous treatment of materials which heretofore it is has been possible to dry or heat only in a non-continuous manner.

In the heat-treatment of certain classes of a materials, for example filter-press cakes, litho one reen cake, etc., it is the practice to e act this in stationary shelf-driers by the aid of direct or indirect heat. It is common practice to separately dry materials 4 in stationary an driers with direct or indirect heat an subsequently dump the dried 16 materials from the receptacles or trays in which they were dried and then to transfer the dried materials into heating apparatus, more commonly known as muffiing furnaces, which are usually hand-operated, and there 0 heat the materials while lying in aquiescent state, except for occasional stirring by means of handoperated paddles or bars, for a definite period of time at a specific temperature. After such treatment, the materials are usually withdrawn from the furnaces by hand into quenching apparatus where they are quickly drowned in water to prevent oxidation.

It is well reco ized in the industry that the above OPGI'ZilZlOII is not entirely eflicient. In the usual hand muflie, above referred to, the material to be muffled with the exclusion Jf air, is unevenly heated. That portion of the material that touches or lies in close proximity to the hot floor or walls of the muflle and also that portion of the charge that is most directly exposed to the heat radiated from the roof of the muffle may be excessively heated while other portions may receive an insufficient amount of heat or at least a considerably smaller amount of heat than the aforementioned portions. Continuous stirring or frequent intermittent stirring is out of the question since entrance of air through the doors would cause oxidation and would detrimentally affect the quality of the material. No satisfactory compromise by which 'suflicient stirring with exclusion of air may be effected, is possible by the old mode of operation above mentioned. y

It is the-primary object of the lIlVEIltlOn to provide an apparatus for and a mode of heat-treating material of the type above referred to in a continuous manner in such a 'way that the material is substantially unibodiment of the furnace.

In the drawing is illustrated a furnace resembling in a general way certain wellknown types of ore roasting and calcining furnaces. The furnace which may be cylindrical is rovided with a combustion chamber 1 sultably connected in a well known manner by fiues with a series of fire-Hues 2, 3, 4, which with the combustion chamber serve to heat the material compartments or shelves 5, 6, 7 and the auxiliary shelf 8, respectively.

Each of the heating compartments is provided' with rabbles 9 which rake the material under treatment and effect its progressive movement from the top of the furnace to the bottom, as is well understood in the metallurgical industry. Thus the material is fed at the center onto the shelf 7 through the chute 10 and is moved outwardly across the sloping shelf 7 by the rabbles to the peripheral passages 11 through which it descends to the shelf or compartment 6. The rabbles in this compartment advance the material toward the center chute 12 whereby it is transferred to the compartment 5, and so on until the material is finally discharged from the furnace as by means of chutes 13.

The rabble-arms are connected to a hollow rotatable tube 14 disposed centrally of the furnace, and the tube is rotated at the desired speed through suitable drivingmechanism indicated generally at 15 and a connecting tubular support 16. Suitable lands or stuffing-boxes 17 are provided at t e top and bottom between the rotating tube an the stationary parts of the furnace.

Air, or in some instances a neutral or. even a reducing gas, is admitted to the tube 14 at its lower end and becomes heated in its xupward travel through contact with the tube and rabble-arms.

Above the upper lire-flue 4 an auxiliary shelf 8 is provided. In the closed compartment 19, of which shelf 8 forms the bottom,-

suitable rakes or rabbles 20 are provided and rotation of the rabble-arms is efi'ected by means of the rotatable-tube 14 to which they are connected. The material to be treated which is preferably introduced at some point along the periphery of the shelf 8 as slurry or pulp coming from a filter press 19 or the like is continuously advanced to the central chute 10 whereby it is introduced into the furnace proper, as above indicated. The heated air or gas rising through the tube 14 is propelled by a blower 21 through pipes 22 and 23 to the shelf 8, and is removed at the opposite side through the stack 24:. I

Numeral 25 indicates a suitable quenching-tank which may be provided with a stirrer 26 and a level controlling float 27.

Part or all of the gases may be withdrawn from the heating compartments, and for this purpose suitable outlets 28, 29 are provided.

In the use of the apparatus described, for example for the drying and heating of green lithopone containing usually about water, the material in wet, sticky condition is fed continuously to the outer edge of the auxiliary shelf 8 and is advanced toward the center chute 10 by the revolving rabbles. During its passage across the shelf the raw lithopone is subjected to hot gas introduced through pipe 23. This operation serves to dry the material, orlitbopone in particular, and enables the lithopone to be fed directly to the calcining chambers in a dry condition and without access of air, the mufliles of the furnace being preferably kept under a plus pressure to prevent entrance of air from the outside. Arriving on the hearth 7 the rabbles 9 rake and distribute the material and move it progressively to the peripheral chutes 11 which convey it to the outer edge of the shelf next below across which it is advanced by the rabbles 9 to the center chute 12, and so on until the lithopone has traversed all of the heating compartments when it is finally discharged through the chutes 13 into one or more quenching tanks 25.

It will be understood that the number of shelves may be varied to meet the requirements of the particular use of the apparatus and that other details may be variously and considerably modified.

The proposed apparatus and method make it, pomible to more completely prevent the access of air and oxygen to the interior of the muflie since the rabbliug is done without the necessity of opening any doors. further prevents the material from becoming over-heated locally on account of the mass of material in the mutfle being constantly moved and mixed by the rabbles so that no portion of the mass remains in the,

hotter localities of the furnace long enough to become superheated. It also accomplishes a very thorough mixing, thereby improving the evenness and bettering the quality of the material by making it thoroughly homogeneous so that in the product fromthis apparatus there is no over-roasted or segregated material which would make the product locally vary in chemical or physical properties.

The apparatus is particularly advanta' geous for handling materials which requires the exclusion of air from the heating chambers during the heating operation, such as is the case with lithopone. Where a combination drying and heating operation is carried out, the auxiliary shelf provides an eflicient and highly economical means of reducing the moisture content of the wet material fed to the furnace.

I am fully aware that the type of furnace by means of which I carry out the objects of the invention is generally well known and I do not claim any novelty in regard to the details of the furnace proper. I have selected this type of furnace merely because it is particularly well adapted for -.the purposes of the invention. The salient ing on the entire drying and calciningthereof as one continuous operation in one vessel.

2. The process of making lithopone which comprises filtering lithopone slurry and then carrying on the entire drying and calcining thereof as one continuous operation in one vessel.

In testimony whereof I afiix my signature.

WALTER G. GRAVES. 

